The present invention relates generally to shielding devices for minimizing the electromagnetic interference and susceptibility effects on electrical and electronic devices and relates especially to such shielding devices consisting of a strip of resilient metal.
It is highly desirable to provide electronic shielding for structures such as test rooms and for enclosures for radio transmitters, radio receivers, computers and other equipment requiring electronic shielding. Such structures often have movable or removable members provided in the form of doors, access panels, drawers, or other non-fixed portions of the structures. Additionally, fixed joints for the structures may also involve permanent connections, attached panels, and other connections which are not readily removable. It is highly desirable to seal these joints effectively against electromagnetic interference and susceptibility effects with a conductive member that permits a dissipation of electrical charges and fields and thereby isolates an offending circuit from a structure to be shielded.
A variety of devices have been prepared for shielding such fixed and movable joints, but these proposals have not been entirely satisfactory. If the shielding device is configured of metal, especially beryllium copper, it has heretofore been difficult or impossible to readily conform the device to an irregular configuration. Since the prior art shielding strips could not be readily curved (after manufacture) to form a rounded corner, special corner sections are typically provided by the manufacturer. As a result, the passageway to be sealed by the shielding device of the known constructions has to have a particular predetermined configuration corresponding to the available corner sections.
Another problem or disadvantage of the prior art shielding devices is the frequent requirement of some sort of fastening or attachment device. Typically, these fasteners consist of double-sided adhesive strips, screws, rivets or other mechanical fastening mechanisms. These fasteners sometimes necessitate special insertion tools and frequently result in increased cost and increased time for attachment to the structure to be shielded.
One form of prior shielding arrangement is disclosed in U.S. Pat. No. 3,277,230, issued on Oct. 4, 1966 to Stickney et al. The Stickney et al patent discloses an electronic shielding gasket that includes a linear metallic strip having a center portion with holes provided therealong and fingers extending in rows along opposite edges of the center portion of the gasket. A special fastening device is required in order to secure the gasket to a supporting surface. The Stickney et al gasket requires a substantial portion of the surface area of the passageway closure due to the lateral extent of the fingers forming part of the gasket.
Another known shielding arrangement is disclosed in U.S. Pat. No. 3,904,810, issued on Sept. 9, 1975 to Kraus. The Kraus patent discloses an electrically conductive contact spring strip that includes a row of parallel spring elements, each of which has a protuberance located on its anterior and posterior surfaces, respectively. An additional mounting structure is required in order to secure the spring strip to its mounting surface. A further limitation of this shielding arrangement is the degree of electrical contact provided by the arrangement of protuberances on the spring elements.
Other types of electromagnetic shielding arrangements including linear metallic strips arranged upon one of two opposing surfaces are disclosed in U.S. Pat. No. 3,504,095, issued on Mar. 31, 1970 to Roberson et al and in IBM Technical Disclosure Bulletin Vol. 12, No. 3, p. 413, (August, 1969); Vol. 13, No. 10, p. 3095, (March, 1971); and Vol. 14, No. 8, p. 2534, (January, 1972). Another prior art patent disclosing an electromagnetic interference and shielding device is U.S. Pat. No. 4,115,655 which issued on Sept. 19, 1978 to Prentice.
Accordingly, it is an object of the present invention to provide an electromagnetic shielding device which can readily conform to an irregular configuration.
Another object of the present invention is to provide an electromagnetic shielding device which is attachable to one member of the structure to be shielded without the use of a separate mechanical fastener.
Still another object of the present invention is to provide an electromagnetic shielding device which is effective to obtain and retain good electrical contact between the surfaces of two relatively movable members even after repeated openings and closings of the members.
A further object of the present invention is to improve the mounting of the shielding device on one of the opposed surfaces whereby the configuration of the mounting arrangement of the shielding device provides and insures good electrical contact with the opposed surfaces without interference by a fastener located between the opposed surfaces being bridged by the shielding device.
Still a further object of the present invention is to provide an electromagnetic shielding device in strip form of metal which is configured so as to permit placement along a wide variety of surface contours.
Yet still another object of the present invention is to provide an electromagnetic shielding device which is relatively inexpensive to manufacture and easy to install such that no tools or special equipment are required to effect installation.
These and other objects are accomplished by an electromagnetic shielding device in accordance with the present invention including a continuous metallic strip defining a plurality of fingers and a base portion. Each of the fingers is joined at one end to the base portion and has a free end which extends in a curved configuration over the base portion. The base portion defines a plurality of segments each having a free end.